Method for automatically sorting the neighbor list of a cell in a communications system

ABSTRACT

A method of automatically prioritizing cells in a neighbor list of a communications system. The priority is defined as the number of times a cell in the neighbor list has been added to the active set. Cells that have been added to the active set more often are given a higher priority. Such higher priority cells are considered first for addition to the monitored set because they are more likely to successfully move from the monitored set to the active set.

FIELD OF THE INVENTION

[0001] The present invention relates generally to the field ofcommunication systems, and more particularly, to a method of sorting theneighbor list of a cell in a communications system.

BACKGROUND OF THE INVENTION

[0002] As shown in FIG. 1, a Universal Mobile Telecommunications System(UMTS) 100 includes a Universal Terrestrial Radio Access Network (UTRAN)in communication with User Equipment (UE). The UTRAN includes a RadioNetwork Controller (RNC). Further details regarding the UMTS can beascertained from sections 5 and 6 of 3GPP TS 25.401 v4.0.0 (2001-03).

[0003] In the UMTS, the UE communicates with the UTRAN via cells toexchange of user information. In the UMTS, a cell is defined as a RadioNetwork object that can be uniquely identified by a UE from a cell IDthat is broadcasted over a geographical area. In an effort to maintaincontinuous communication with the UTRAN, the UE monitors four sets ofcells—the Active Set, Monitored Set, Detected Set and Virtual ActiveSet. The Active Set includes UTRAN cells with which the UE is in soft orsofter handover with. Cells within the Active Set are active cells,while those not in the Active Set are non-active cells. User informationis exchanged between the UE and UTRAN through the active cells. TheActive Set contains only UTRAN cells and the cells are all under thesame UMTS frequency.

[0004] The Monitored Set includes cells not currently in the Active Setthat the UE is monitoring for handover according to a neighbor listassigned by the UTRAN. The Monitored Set may contain UTRAN and GlobalSystem for Mobile Communications (GSM) cells. The UTRAN cells may beunder different UMTS frequencies. The Detected Set includes cells thatare not in the Active Set or Monitored Set, but which are detected bythe UE without RNC direction. In other words, the UE discovers thesecells on its own, rather than according to a neighbor list assigned bythe UTRAN. The UE reports only detected cells (UTRAN cells only) thatare under the same frequency as the active cells (used frequency) andonly when in a particular state. The Virtual Active Set is an Active Setassociated with a non-used frequency. Cells in the Virtual Active Setare UTRAN cells that the UE is measuring for potential inter-frequencyhandover (hard handover). These cells are managed as a virtual activeset using intra-frequency measurement criteria and events. Afterexecution of the hard handover, the Virtual Active Set becomes theActive Set.

[0005] Each cell in the Active Set has a neighbor list of cells thatincludes cells that are likely candidates for handover. These cells areused to construct the Monitored Set. Currently, cells in the neighborlist are prioritized by the system operator when the list isprovisioned. The priority may or may not be based on the likelihood ofthe cells being promoted to the Active Set. Thus, there is a need for amethod of automatically ordering the neighbor list of a cell in theActive Set according to the likelihood that the cell will be promoted tothe Active Set.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1 is a block diagram of a system that can be used toimplement the preferred embodiment of the present invention.

[0007]FIGS. 2A and 2B are a flow diagram of the preferred embodiment ofthe method of the present invention.

[0008]FIG. 3 is an example of the method of FIG. 2 when a cell C isadded to the active set immediately after system startup.

[0009]FIG. 4 is an example of the method of FIG. 2 when cell C is addedto the active set some time after system startup but before the firstswap of counter set A and counter set B.

[0010]FIG. 5 is an example of the method of FIG. 2 when cell C is addedto the active set some time after system startup but before the firstswap of counter set A and counter set B, with counter set A reaching itsmaximum value.

[0011]FIG. 6 is an example of the method of FIG. 2 when cell C is addedto the active set some time after the first swap of counter set A andcounter set B.

[0012]FIG. 7 is an example of the method of FIG. 2 when cell C is addedto the active set some time after the first swap of counter set A andcounter set B, with the neighbor list counter for counter set B reachingits predetermined value.

[0013]FIG. 8 is an example of the method of FIG. 2 when a cell M isadded to the active set some time after the first swap of counter set Aand counter set B, with a cell counter in counter set B reaching itsmaximum value.

[0014]FIG. 9 is an example of prioritized neighbor lists for cells P, Qand R that are used to assemble a monitored list for the UE of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

[0015] The present invention provides a method of automaticallyprioritizing the order of cells in a neighbor list. In the preferredembodiment, the cells are prioritized based on the number of times acell in the neighbor list has been added to the active set while theowner of the neighbor list is in the active set. A cell that has beenadded to the active set the most is given the highest priority. A cellthat has been added to the active set the least is given the lowestpriority. The higher priority cells are considered first for addition tothe monitored set because they are more likely to be promoted from themonitored set to the active set. The method of the present inventionsimplifies ordering of the neighbor list by automating the process. Thissimplification, in turn, leads to the reduction of dropped calls andalso improves the quality of communications. Automatic ordering allowsthe cells that are most frequently added to the active set to increaseits priority in the neighbor list. This greatly increases the chancesthat those cells will be included in the monitored set. While the systemoperator may make a first best guess when provisioning the database, theautomatic ordering fine tunes that guess to ensure that the cells addedmost successfully to the active set are included in the monitored set.By implementing an ongoing process, the system can self adjust tochanging conditions.

[0016] The preferred embodiment of the automated sorting method of thepresent invention is described with reference to a UMTS. However, itwill be appreciated by one of ordinary skill in the art that theinvention can be implemented in any communications system. Referring toFIG. 1, in the UMTS 100, the method is implemented in the RNC 104 by anymicroprocessor or computer commonly known in the art. The method isperformed on an individual neighbor list basis and is controlled by thevalue of a parameter called “Neighbor List Auto Sort.” If the NeighborList Auto Sort parameter is enabled for a particular neighbor list, thatneighbor list will be sorted in accordance with the invention. If theparameter is disabled, the order of the neighbor list as stored in theRNC's database (not shown) will be used. Typically, the system operatorspecifies the order of the neighbor list when the list is provisioned.

[0017] In establishing the priority for automatic sorting, the methoduses a cell counter for each cell within each neighbor list to track thenumber of times the cell is added to the active set while the owner ofthe neighbor list is in the active set. Collectively, the cell countersfor the cells in a particular neighbor list are referred to as a counterset. In the preferred embodiment, each cell in a neighbor list has twocounters. Because each counter can count to a finite maximum value, thecounters are duplicated to prevent an overflow situation. Thus, themethod uses to counter sets to track the number of times cells in aneighbor list are added to the active set. Herein, the counter sets arereferred to as counter set A and counter set B. As will be describedwith reference to FIG. 2 later herein, only counter set A or counter setB is active at any given time. If the active cell counters for aneighbor list is counter set A, counter set B is considered standby.Likewise, if the active cell counters for a neighbor list is counter setB, counter set A is considered standby. When any individual cell counterin a counter set (A or B) reaches its maximum value, the standby counterset is cleared and the active and standby counter sets are swapped. Inother words, if a counter in counter set A reaches its maximum value,counter set B is cleared and becomes the active counter set. Thisswapping of the counters continues throughout the process each time anindividual cell counter in a counter set reaches its maximum value.

[0018] In addition to each neighbor list having two cell counter sets,each neighbor list has two neighbor list counters—a neighbor listcounter for counter set A and a neighbor list counter for counter set B.The neighbor list counter keeps track of the number of times any cell inthe counter set (A or B) is added to the active set. After systemstartup, the cell counter sets and neighbor list counters are set tozero. To produce an accurate priority sorting of a cell's neighbor list,the method of the present invention prioritizes the list when one of theneighbor list counters reaches a predetermined value, preferably fivehundred (500). In this manner, the method waits until the cells in aneighbor list have been added to the active set 500 times (collectively)before prioritizing the list. Until the neighbor list counter reachesthe predetermined value, the order of cells in a neighbor list isobtained from a database in the RNC 104 (FIG. 1).

[0019] Referring to the flowchart of FIGS. 2A and 2B (referred tocollectively as FIG. 2), the method of the present invention begins whena cell is added to the active set. At step 202, the method begins. Atstep 204, the method determines whether the cell was added to the activeset immediately after system startup. If the answer is yes, at step 206,the method initializes all neighbor list counters and cell counters(counter set A and counter set B) to zero. Also, the method initializesthe active cell counters as counter set A and the standby cell countersas counter set B. Finally, the method prioritizes all neighbor listsaccording to the order in the RNC database. At step 208, the methodinitializes a variable “i” to 1. Variable “i” is used as a pointer to aparticular cell already in the active set. In the first instance at step208, “i” points to the first cell already in the active set.

[0020] At step 210, the method determines whether the cell just added tothe active set (cell_(a)) is in the neighbor list of the first cellalready in the active set (cell_(i), where i=1). If cell_(a) is not inthe neighbor list of cell_(i), the method determines whether “i”currently points to the last cell (N) already in the active set (step230). If the answer is yes, the method ends at step 234. If the answeris no, the method increments “i” (step 232) and proceeds to step 210 tocontinue determining whether cell_(a) is in the neighbor list of othercells already in the active set. At step 210, if the method determinesthat cell_(a) is in the neighbor list of cell_(i), it increments theactive cell counter (at this point, counter in counter set A) associatedwith celia in the neighbor list of cell_(i). Next, at step 214, themethod determines whether the counter incremented in step 212 hasreached its maximum value. If the counter incremented in step 212 hasreached its maximum value, at step 215, the method increments theneighbor list counter for the active counter set. At step 216, themethod prepares to swap the active and standby counters. In particular,the method clears each standby cell counter (at this point, counter setB) associated with the cells in the neighbor list of cell₁ (step 216).At step 216, the method also clears the standby neighbor list counterfor the neighbor list of cell_(i). At step 218, for the neighbor list ofcell_(i), the method swaps the active and standby counters. At thispoint, counter set A becomes standby and counter set B becomes active.(Of course, later in the process the situation may be different andcounter set B would again become standby and counter set A would againbecome active.) From step 218, the method proceeds to step 224. Step 224is described in the next paragraph.

[0021] Referring back to step 214, if the method determines that thecounter incremented in step 212 has not reached its maximum value, itincrements the active neighbor list counter for the neighbor list ofcell_(i) (step 220). At step 222, the method determines whether theneighbor list counter incremented in step 220 has reached thepredetermined value. If the answer is yes, at step 226, the methodprioritizes the order of the neighbor list of cell_(i) based on theactive cell counters (counter set A or counter set B). Next, the methodproceeds to step 230 and continues processing as previously described.If at step 222 the answer is no, the method proceeds to step 224. Atstep 224, the method determines whether the standby neighbor listcounter for the neighbor list of cell_(i) has reached its predeterminedvalue. If the answer is no, the method proceeds to step 230 andcontinues processing as previously described. It should be noted thatwhen neither of the active or standby cell counters can be used toprioritize the neighbor list, the priority is based on the order in theRNC 104 (FIG. 1) database.

[0022] Referring back to step 224, if the standby neighbor list counterfor the neighbor list of cell_(i) has reached its predetermined value,at step 228, the method prioritizes the order of the neighbor list ofcell_(i) based on the standby cell counters (counter set A or B). Next,the method proceeds to step 230 and continues processing as previouslydescribed.

[0023] Once the method has prioritized all “N” neighbor lists, theMonitored Set can be constructed. In the preferred embodiment, whenevera new Monitored Set is constructed for a MS, the neighbor lists for allcells in the Active Set are concatenated in a round robin fashion usingan order based on the priority of the cells in each neighbor list. Thistechnique is illustrated in the examples that follow.

[0024] FIGS. 3-8 provide examples of the method of the present inventionin accordance with the flowchart of FIG. 2 when a cell is added to theactive set under different conditions. For simplicity of explanation,the following assumptions are made: (1) cell P is the first cell alreadyin the active set; (2) the maximum value for the cell counters is 300;and (3) the predetermined value for the neighbor list counters is 500.

[0025]FIG. 3 provides an example of the method when a cell C is added tothe active set immediately after system startup. According to the flowchart of FIG. 2, the method follows the “yes” path at step 204. At step206, the method initializes all neighbor list counters and cell counters(counter set A and counter set B) to zero, and initializes the activecell counters as counter set A and the standby cell counters as counterset B. This is shown in block 302 of FIG. 3. At step 208, variable “i”is initialized to 1 to point to cell P. At step 210, the methoddetermines that cell C is in the neighbor list of cell P. At step 212,the method increments counter set A in cell P's neighbor list. Morespecifically, the method increments the cell counter associated withcell C in cell P's neighbor list. This is shown in block 304 of FIG. 3.At step 214, the method determines that the cell counter associated withcell C has not reached its maximum value. At step 220, the methodincrements the active neighbor list counter (counter set A) for cell P'sneighbor list. This is shown in block 304 of FIG. 3. At steps 222 and224, the method determines that both the counter set A and counter set Bneighbor list counters are less than the predetermined value, preferably500. Because both of the neighbor list counters are less than thepredetermined value, the neighbor list of cell P is prioritized based onthe database in the RNC 104 of FIG. 1. As shown in block 304 of FIG. 3,the prioritization is D, C, M.

[0026]FIG. 4 provides an example of the method when cell C is added tothe active set some time after system startup but before the first swapof counter set A and counter set B. In accordance with the flowchart ofFIG. 2, at step 204, the method determines that system startup did notjust occur. At step 208, variable “i” is initialized to 1 to point tocell P already in the active set. At step 210, the method determinesthat cell C is in the neighbor list of cell P. At step 212, the methodincrements counter set A in cell P's neighbor list. More specifically,the method increments the cell counter associated with cell C in cellP's neighbor list. This is shown in blocks 402 and 404 of FIG. 4 by cellC's counter increasing from 275 to 276. At step 214, the methoddetermines that the cell counter associated with cell C has not reachedits maximum value. At step 220, the method increments the activeneighbor list counter (counter set A) for cell P's neighbor list. Thisis shown in blocks 402 and 404 of FIG. 4 by the neighbor list counterfor counter set A increasing from 673 to 674. At step 222, the methoddetermines that the neighbor list counter for counter set A of cell P'sneighbor list is greater than the predetermined value. At step 226, themethod prioritizes the order of cell P's neighbor list based on counterset A. Namely, the priority order is C, M, D.

[0027]FIG. 5 provides an example of the method when cell C is added tothe active set some time after system startup but before the first swapof counter set A and counter set B. In this example, a cell counter incounter set A reaches its maximum value of 300. In accordance with theflowchart of FIG. 2, at step 204, the method determines that systemstartup did not just occur. At step 208, variable “i” is initialized to1 to point to cell P already in the active set. At step 210, the methoddetermines that cell C is in the neighbor list of cell P. At step 212,the method increments counter set A in cell P's neighbor list. Morespecifically, the method increments the cell counter associated withcell C in cell P's neighbor list. This is shown in blocks 502 and 504 ofFIG. 5 by cell C's counter increasing from 299 to 300. At step 214, themethod determines that the cell counter associated with cell C hasreached its maximum value. At step 215, the method increments theneighbor list counter for counter set A. At step 216, the method clearsthe counters in counter set B (in this case, counter set B was alreadyzero) of cell P's neighbor list. The method also clears the neighborlist counter for counter set B. At step 218, for cell P's neighbor list,the method makes counter set B (cell counters and neighbor list counter)the active counter and counter set A the standby counter. This is shownin block 504 of FIG. 5. At step 224, the method determines that theneighbor list counter for counter set A is greater than thepredetermined value and prioritizes the order of cell P's neighbor listbased on counter set A (step 228). According to block 504 in FIG. 5, theorder is C, M, D.

[0028]FIG. 6 provides an example of the method when cell C is added tothe active set some time after the first swap of counter set A andcounter set B. In accordance with the flowchart of FIG. 2, at step 204,the method determines that system startup did not just occur. At step208, variable “i” is initialized to 1 to point to cell P already in theactive set. At step 210, the method determines that cell C is in theneighbor list of cell P. At step 212, the method increments counter setB in cell P's neighbor list. More specifically, the method incrementsthe cell counter associated with cell C in cell P's neighbor list. Thisis shown in blocks 602 and 604 of FIG. 6 by cell C's counter increasingfrom 19 to 20. At step 214, the method determines that the cell counterassociated with cell C has not reached its maximum value. At step 220,the method increments the active neighbor list counter (counter set B)for cell P's neighbor list. This is shown in blocks 602 and 604 of FIG.6 by the neighbor list counter for counter set B increasing from 399 to400. At step 222, the method determines that the neighbor list counterfor counter set B is below the predetermined value. At step 224, themethod determines that the neighbor list counter for counter set A isabove the predetermined value and thus uses counter set A to prioritizecell P's neighbor list. According to FIG. 6, the order is C, M, D.

[0029]FIG. 7 provides an example of the method when cell C is added tothe active set some time after the first swap of counter set A andcounter set B. In this example, the neighbor list counter for counterset B reaches the predetermined value of 500. In accordance with theflowchart of FIG. 2, at step 204, the method determines that systemstartup did not just occur. At step 208, variable “i” is initialized to1 to point to cell P already in the active set. At step 210, the methoddetermines that cell C is in the neighbor list of cell P. At step 212,the method increments counter set B in cell P's neighbor list. Morespecifically, the method increments the cell counter associated withcell C in cell P's neighbor list. This is shown in blocks 702 and 704 ofFIG. 7 by cell C's counter increasing from 50 to 51. At step 214, themethod determines that the cell counter associated with cell C has notreached its maximum value. At step 220, the method increments the activeneighbor list counter (counter set B) for cell P's neighbor list. Thisis shown in blocks 702 and 704 of FIG. 7 by the neighbor list counterfor counter set B increasing from 499 to 500. At step 222, the methoddetermines that the neighbor list counter for counter set B is equal tothe predetermined value. At step 226, the method uses the values ofcounter set B to prioritize cell P's neighbor list as M, D, C.

[0030]FIG. 8 provides an example of the method when a cell M is added tothe active set some time after the first swap of counter set A andcounter set B. In this example, a cell counter in counter set B reachesthe maximum value of 300. In accordance with the flowchart of FIG. 2, atstep 204, the method determines that system startup did not just occur.At step 208, variable “i” is initialized to 1 to point to cell P alreadyin the active set. At step 210, the method determines that cell M is inthe neighbor list of cell P. At step 212, the method increments counterset B in cell P's neighbor list. More specifically, the methodincrements the cell counter associated with cell M in cell P's neighborlist. This is shown in blocks 802 and 804 of FIG. 8 by cell M's counterincreasing from 299 to 300. At step 214, the method determines that cellM's counter in counter set B has reached the maximum value. At step 215,the method increments the neighbor list counter for counter set B. Thisis shown in blocks 802 and 804 of FIG. 8 by the neighbor list counterincreasing from 500 to 501. At step 216, the method clears the countersin counter set A of cell P's neighbor list. The method also clears theneighbor list counter for counter set A. At step 218, for cell P'sneighbor list, the method makes counter set A (cell counters andneighbor list counter) the active counter and counter set B the standbycounter. This is shown in block 804 of FIG. 8. At step 224, the methoddetermines that the neighbor list counter for counter set B is greaterthan the predetermined value and prioritizes the order of cell P'sneighbor list based on counter set B (step 228). According to block 804in FIG. 8, the order is M, D, C.

[0031] For simplicity of explanation, the examples of FIGS. 3-8 assumedthat the UE 106 (FIG. 1) had only one cell (cell P) already in itsactive set. Thus, the monitored set is created using the prioritizedneighbor list for cell P. Using the results of the example in FIG. 8,the Monitored set includes cells M, D, C. The UE 106 may have multiplecells, such as cells P, Q and R, already in its active set. The neighborlists of cells Q and R would have their own unique priority order ofcells, such as M, C, P and D, Q, M, respectively, as shown in FIG. 9. Inthis case, a round robin selection from neighbor lists P, Q and R wouldbe used to assemble the monitored list. For example, selecting from eachlist, the monitored list would include: (1) cell M (the highest prioritycell in the neighbor list of cell P); (2) cell C (the second highestpriority cell in the neighbor list of cell Q because the highestpriority cell M has already been included in the monitored list); andcell D (highest priority cell in the neighbor list of cell R).

[0032] While the invention may be susceptible to various modificationsand alternative forms, a specific embodiment has been shown by way ofexample in the drawings and has been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modification, equivalents and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims. For example, changes in system configuration, such asthe removal of a cell from a neighbor list, may make it desirable torestart the prioritization process manually. A user command may beprovided for this purpose. Such a command could force a swap of theactive and standby counters (cell counters and neighbor list counters)and force a reset of the appropriate counters. Such action could be usedto force the system to user the priority order provided in the RNCdatabase.

What is claimed is:
 1. A method of prioritizing a plurality of cells ina neighbor list of a cell in an active set comprising the steps of: foreach cell of the plurality of cells, tracking an amount of times thecell of the plurality of cells is added to the active set; tracking anamount of times any cell of the plurality of cells is added to theactive set; and when the plurality of cells have been added to theactive set a predetermined amount of times, prioritizing the pluralityof cells in the neighbor list.
 2. The method of claim 1 wherein the stepof tracking when a cell of the plurality of cells is added to the activeset comprises: maintaining a first counter set for the plurality ofcells, wherein the first counter set comprises a counter for each of theplurality of cells; and incrementing the counter in the first counterset corresponding to the cell that is added to the active set.
 3. Themethod of claim 2 wherein the step of tracking when any cell of theplurality of cells is added to the active set comprises: maintaining asecond counter for the neighbor list; and incrementing the secondcounter when any cell of the plurality of cells in the neighbor list isadded to the active set.
 4. The method of claim 3 wherein the step ofprioritizing comprises: when the second counter reaches a predeterminedvalue, ordering the plurality of cells in the neighbor list from ahighest priority to a lowest priority, wherein the cell associated withthe counter in the first counter set having a highest value is given thehighest priority and the cell associated with the counter in the firstcounter set having a lowest value is given the lowest priority.
 5. Themethod of claim 1 wherein the step of tracking the amount of times thecell of the plurality of cells is added to the active set comprises:maintaining a plurality of counter sets for each cell of the pluralityof cells, wherein each of the plurality of counter sets comprises aplurality of counters corresponding to the plurality of cells andwherein a first counter set of the plurality of counter sets is activeand a second counter set of the plurality of counter sets is standby;and incrementing the counter in the active counter set corresponding tothe cell that is added to the active set.
 6. The method of claim 5wherein the step of tracking when any cell of the plurality of cells isadded to the active set comprises: maintaining a plurality of neighborlist counters, wherein a first neighbor list counter is active and asecond neighbor list counter is standby; and incrementing the activeneighbor list counter when any cell of the plurality of cells in theneighbor list is added to the active set.
 7. The method of claim 5further comprising the steps of: determining whether the counter in theactive counter set corresponding to the cell that is added to the activeset has reached a maximum value; and if the counter has reached themaximum value, incrementing the active neighbor list counter; clearingthe standby counter set; clearing the standby neighbor list counter;swapping the active and standby counter sets swapping the active andstandby neighbor list counters.
 8. In a communications system whereinuser equipment monitors a plurality of cells in a plurality of neighborlists for inclusion in a monitored set and subsequent promotion to anactive set, a method of prioritizing the plurality of cells in theplurality of neighbor lists comprising the steps of: detecting when anew cell has been added to the active set; for each cell_(i)already inthe active set, determining whether the new cell is included in theneighbor list of cell_(i); if the new cell is included in the neighborlist of cell_(i), incrementing a counter in a first counter setassociated with the new cell in the neighbor list of cell_(i);determining whether the counter in the first counter set has reached amaximum value; if the counter in the first counter set has not reachedthe maximum value, incrementing a first neighbor list counter associatedwith the neighbor list of cell_(i); determining whether the firstneighbor list counter has reached a predetermined value; if the firstneighbor list counter has reached the predetermined value, prioritizingthe plurality of cells in the neighbor list of cell_(i); andconstructing the monitored set from the plurality of cells in theplurality of neighbor lists.
 9. The method of claim 8 wherein the firstcounter set is active and the plurality of cells in the neighbor list ofcell_(i) has a second counter set that is standby, wherein the firstneighbor list counter is active and each neighbor list of cell_(i) has asecond neighbor list counter that is standby, and wherein if a counterin the active counter set has reached the maximum value, the methodfurther comprises the steps of: incrementing the active neighbor listcounter associated with the neighbor list of cell_(i); clearing thestandby counter set of the plurality of cells in the neighbor list ofcell_(i); clearing the standby neighbor list counter of the neighborlist of cell_(i); swapping the active and standby counter sets; swappingthe active and standby neighbor list counters; determining whether thestandby neighbor list counter for the neighbor list of cell_(i) hasreached a predetermined value; and if the standby neighbor list counterhas reached the predetermined value, prioritizing the plurality of cellsin the neighbor list of cell_(i).
 10. An apparatus for prioritizing aplurality of cells in a neighbor list of a cell in an active setcomprising: a radio network controller; and a processor running in theradio network controller wherein the processor when operative isconfigured to for each cell of the plurality of cells, track an amountof times the cell of the plurality of cells is added to the active set;track an amount of times any cell of the plurality of cells is added tothe active set; and when the plurality of cells have been added to theactive set a predetermined amount of times, prioritize the plurality ofcells in the neighbor list.